The production of titanium tetrachloride (“TiCl4”) via the chlorination of titanium values in a titanium-containing starting material is generally known in the art. The production of TiCl4 is useful, for example, in the production of titanium metal or titanium dioxide (“TiO2”).
As is known in the art, TiCl4 can be produced by reacting chlorine gas with titanium-containing starting materials, typically in a fluid bed chlorinator. Titanium dioxide-containing ores used as starting materials contain a variety of impurities, notably including oxides of Fe, Mn, Ni, Si, Al, Nb, Zr, V, Mg, and Ca. Most of the impurities are chlorinated with the TiO2 in the ore, and form volatile chlorides at the temperatures that typically characterize the chlorination process (that is, from about 800° C. to about 1400° C.).
The off-gases from the chlorination process comprise a gaseous mixture including CO, CO2, TiCl4, N2, and Cl2. The gaseous mixture also contains the volatile chlorides of the impurities discussed above as well as some residual solids (typically also chlorides) that are carried out of the chlorinator due to entrainment. The solids-laden gaseous mixture is conventionally transported through a duct from the top of the chlorinator to a device, for example, a cyclone, which separates solids from the gases. The ductwork between the chlorinator and the cyclone is frequently referred to as a crossover or chlorinator crossover.
As the gaseous mixture is transported to the cyclone through the ductwork, the gases cool, causing some of the chlorides to condense as tacky solids. The tacky solids can build up on the internal surface of the ductwork, creating blockage to the extent that the blockage can cause a pressure drop through the duct. If the pressure drop becomes too high the process may not be economical to operate, requiring a shutdown to clean the duct (for example, by sand blasting or through the use of mechanical devices such as chain flails) or change ducts. Decreasing or preventing the tacky solids build up and consequent blockage would allow longer run times between shutdowns and also allow usage of lower grade ores containing greater quantities of impurity metal oxides. Attempts have been made to cool the gaseous mixture rapidly before it enters the ductwork, but this approach requires major modifications to an existing chlorinator as well as extensive down time.